1. Field of the Invention:
This invention relates to motorized cameras in which film is wound up by an electric motor.
2. Description of the Prior Art:
Recently, as motorization of camera advances, introduction of capabilities of automatic winding-up and rewinding has been proposed. For this purpose, according to the prior art, only one electric motor was used in combination with a torque transmission changeover mechanism or clutch at an intermediate point in the wind-up transmission system so that motion of the motor is switched by the clutch to the rewind transmission system.
But, such a method is associated with:
(1) Since, on the layout of the camera, the motor is necessarily put on the opposite side of the film gate to that on which lies the film cartridge chamber, for, as the distance from the motor to the rewind shaft is very long, the rewind transmission is constructed by a gear train, a great number of gears is required and the efficiency of transmission is poor.
(2) Among the loads on charging, the shutter, focusing lens, mirror drive mechanism are not affected by the change of the ambient temperature, remaining almost constant in load, but the load on the take-up spool varies about 5 times, as the convoluted amount of film thereon varies and the ambient temperature changes. So, the speed reduction ratio of the transmission system must be unduly largely increased. Thus charing cannot be performed with high efficiency.
To eliminate the above-described drawbacks, there has been a previous proposal for employing two motors in the wind-up and rewind transmission systems.
Also, to further enhance the effect of the coexistence of the two motors, for example, an additional proposal has been made that the wind-up transmission system is provided with a low speed transmission system of large speed reduction ratio and a high speed transmission system of small speed reduction arranged upon change of the direction of rotation of the wind-up motor to change the speed reduction ratio of the wind-up transmission system so that as the film differs from cartridge to cartridge, and the temperature changes, and further the electrical power source or battery deteriorates, the speed reduction ratio is changed to suit them. As the method of changing over the speed reduction ratio of the transmission system by reversing the rotation of the motor, the planetary gear changeover method is known, being suited to small size instruments such as cameras from the standpoint of space and cost.
But, the use of the separate motors in winding up and rewinding the film results in that as the wind-up motor with its transmission system is linked by the film to the rewind motor with its transmission system, it is when in the rewind mode that the rewind motor rotates even the wind-up motor and the wind-up transmission system. Particularly when the wind-up transmission system is in the large speed reduction ratio an excessive load is laid on the rewind motor. Also, in some occasion, it will lead to damage the film or like accident.
Also, in connection with the use of the planetary clutch mechanism for changing over the speed reduction ratio of the wind-up transmission system between the large and small values by changing the direction of rotation of the wind-up motor, it should be pointed out that in the motor driven transportation device constructed in such a manner that the planetary clutch mechanism is arranged in the wind-up transmission system to be able to drive two wind-up transmission systems and, besides it, the rewind transmission system is made associated therewith, though it is desirable that when in the rewinding operation, the planetary gears of the clutch mechanism of the wind-up transmission system is set in the neutral position (out of engagement with both transmission systems), in actual practice such setting is difficult to do, because the clutch mechanism is of the planetary gear type. So, as it is unavoidable to set the wind-up transmission system in either one of the values of speed reduction ratio, when in the rewind mode, in order to minimize the load on the rewind motor, it is better to select the small speed reduction or high speed transmission system by the planetary clutch mechanism. And, if it is possible to maintain the setting of the wind-up transmission system in the high speed transmission system until the rewinding is completed, the load on the rewind motor could not become excessive. In actual practice, however, there is a possibility of occurrence of an unintentional switching of the clutch mechanism to the opposite state where the low speed transmission system works at an intermediate point during the rewinding. In more detail, the rewinding with the planetary clutch mechanism in the high speed transmission system causes the take-up spool to rotate in the opposite direction to that in which it rotates when in the wind-up mode as the film is trained between the take-up and supply spools, while the wind-up motor is caused to rotate in the opposite direction to that when in the high speed winding up, or in the same direction when in the slow speed transmission system. For this reason, the wind-up motor works as if it were a fly wheel. So if it happens that the rewinding speed changes due to the change of the load during the rewinding, as the speed of rotation of the wind-up motor overtakes the rewinding speed at a moment when the rewinding speed falls, the aforesaid planetary clutch mechanism will be changed over to select the low speed wind-up transmission system for operation, thereby the load is suddenly changed high at an intermediate point during the rewinding. This produces problems of breaking the perforations of the film and cutting off the film itself.
Besides the above-described arrangement of the two transmission systems of different speed reduction ratio in the wind-up transmission system, any wind-up system having the planetary clutch mechanism between the two transmission systems has the above-described problem that the changing over takes place at a time during the rewinding.